A friend dropped off an old eMachine tower that he complained was running slow on Windows XP Home. Looked at the front of the eMachine and it stated Celeron D 335, so I figured cool, it might support the socket 775 E4300 1.8Ghz Core 2 Duo with 2M Cache that I have laying around and can give him for a free upgrade.

What a disappointment it was to find out that they actually made a Celeron D 2.8Ghz in Socket 478 design. I assumed that all Celeron D and Pentium D's were in socket 775 design. I looked the motherboard up ONLINE to see what CPU's it supported and was surprised that the motherboard was a good quality but low cost/ low featured Intel Motherboard and the most powerful CPU supported in it is a socket 478 Pentium 4 3.4Ghz Extreme Edition. I ENDED up picking up a cheap Pentium 4 3.0Ghz HT 1M/800 socket 478 for $5.95 with free shipping off of ebay last night which is supported by this motherboard and this should make an improvement to its speed with 4x more Cache and HT for 1 physical core + 1 virtual core which acts like a dual-core.

He doesnt have much money and so I am actually buying this CPU out of my own pocket because what is $6 anyways among friends.

Question I have is that his system currently has 333Mhz DDR RAM in it ( 2 x 512MB ) sticks and it supports 400Mhz DDR RAM. Anyone know if its even worth it to try to find ( 2 x 512MB or a single 1GB ) 400Mhz RAM for it?

The multiplier should be fine at 9 x 333 for 2997Mhz for the 3Ghz CPU, but not sure if there is much more to gain in 333 to 400Mhz FSB RAM or not.

I remember a ways back someone brought to me a home built gaming system with 266Mhz FSB RAM in a motherboard that supported 266,333,400 FSB and they had a single 1GB Kingston DDR 266Mhz stick in a motherboard running a Pentium 4 2.8Ghz HT 1M/800 and the multiplier was like 10.5 to match the 2800Mhz and swapping them over to ( *2 x 512MB DDR 400Mhz ) sticks ( *RAM that was pulled from a DOA system but still good ) installed in a motherboard that also supported dual-channel made a world of difference in better performance, BUT... there was 2 beneficial gains 400Mhz vs 266Mhz and Dual-Channel vs Single-Channel. So how much was gained by each benefit which was recognized as a whole when booted.

I asked why they spent the money to build a decent gaming system back almost 10 years ago, and skimped out on the memory speed and they claimed that the guy at this one computer shop offered them a deal that day and they didnt know there was better faster RAM available for it to better match the CPU. They were told that these parts are all compatible and here is the price tag for it all to be custom built. Later on in its use it was showing lag, and thats when it was brought to me to check it out.

A long time ago I remember installing 400Mhz DDR RAM into my Athlon XP 2800+ system in place of the 333Mhz DDR RAM as part of the upgrade from 512MB to 1024MB RAM and I didnt NOTICE any performance gain other than the fact that I could have more applications running at the same time than before. I also though am not sure of the motherboard was running the 400Mhz RAM really downclocked at 333Mhz EITHER to where there is no real speed difference. This motherboard died in 2008 and so I dont have it to look back at to see what the FSB was running at with say CPU-Z etc.

As far as his use of this computer, he plays online games through the low end old computers 64MB shared memory of Intel Extreme Graphics GPU with the 865 chipset, so games on facebook and other online non-graphics intensive games which are turn based for example run ok on it, but the Celeron D running Windows XP Home SP3 on 80GB IDE HDD with 1GB of 333Mhz DDR RAM is lagging pretty badly. I performed a clean factory install and its quick until after all the what must me almost 200 updates to SP3 in which it just crawls because the CPU is WEAK. My daughter has a Pentium 4 2.8Ghz HT which is also a 1M/800 CPU with 1GB of DDR 400Mhz and it runs quite well and can even play some modern games like World of Warcraft 5.4.1, but she also isnt running integrated graphics, she is running on a 8x AGP GeForce 6200 with 256MB RAM so there is no good comparison really other than I know that the P4 HT 3Ghz will be way better than the Celeron D single-core CPU that he has now.
The speed difference going from 333 to 400MHz memory will be unnoticeable, a few benchmarks may show a slight improvement but in the real world, nothing. Definitely don't spend any money on this.
1GB sticks of DDR tend to cost more than they're worth to most people, if you can find 2GB at a reasonable price upgrading to that may be worth it, but unless it's dirt cheap I wouldn't bother.Thanks Calum .... will stick with the 333Mhz RAM then.

And yes this system is not worth much and not really worth putting much money into it. But the CPU upgrade from the Celeron D 335 2.8Ghz with 256k Cache single-core to Pentium 4 HT 3.0Ghz with 1M Cache will make a performance gain since I have upgraded from Celeron to Pentium 4 before to have a feel for what is to be gained.

This is the ebay merchant I went through to get the CPU. I looks like he or she has many of them available for $5.95 with free shipping. http://www.ebay.com/itm/Intel-Pentium-4-3-0-GHz-socket-478-CPU-SL7E4-1M-800-P4-HT-3000-Prescott-/221319931544?pt=CPUs&hash=item3387b22698#ht_1574wt_896

While its nice that old parts are available cheap on ebay for inexpensive upgrades like this one, I was kind of surprised that there still seems to be a good market for 10 year old parts and people buying socket 478 CPUs in bulk etc. I can see a couple sold to people like myself who want to stretch the usable life out of an old computer or two, but to see some auctions for them sold in bulk with a buyer count listed, it makes me wonder who needs these in bulk when its so affordable anymore to build newer. Maybe there is a market for Pentium 4 CPU systems in a poorer region of the world in which a refurb computer is the first family computer and a Pentium 4 is plenty for getting online and can run Windows XP, Vista, or 7 without too much trouble as well as Linux Distros also run well on them with at least 1GB RAM to run with minimal load time lag.

Sometimes I still see Pentium 4 refurb systems for sale on newegg and Tiger Direct for like $120 with Windows 7 Home 32-bit , where at that price tag, the OS itself even if purchased in bulk is a good 75% of the price tag, so the hardware was only valued at like $40. But most of them are Pentium D and early Core 2 Duo's these days.